The present invention relates generally to the field of infusion monitoring and alarm devices. More particularly, the present invention relates to an infusion monitoring apparatus which enables a healthcare provider to be alerted when a predetermined amount of fluid has been infused, or the infusion bag is nearly empty.
Intravenous supply and irrigation systems are widely used in medical treatments to supply and dispense fluids, such as sterile water, nutrients, medicines, saline, blood or blood products, etc. A conventional way to dispense an intravenous fluid is to suspend a supply of the fluid in a bag or bottle above the patient, connect the length of tubing to an outlet of the fluid supply, and deliver the fluid to the patient via the tubing through a needle inserted into the patient. By suspending the fluid supply above the patient, the fluid can be delivered to the patient at a desired pressure.
In some cases, the delivery of such fluids in this manner occurs over a period of several hours. In other instances, the rate of fluid delivery is much quicker. In some situations, it is desired to monitor the delivery of the fluid so that the delivery of the fluid can be stopped before the fluid runs low or so that a new supply of fluid can be provided to maintain an uninterrupted flow to the patient. In other situations, less than a full amount of the fluid supply is desired to be infused.
If a fluid being delivered runs low or even runs out before a nurse or other medical attendant detects the condition, the patient may experience undesirable effects. These undesirable effects can include clotting of the infusion line, introduction of air into the infusion line, improper infusion volume, and so forth. Running out of surgical irrigation fluid can impair visualization of the surgical field and delay surgery while the fluid bag is replaced and air is evacuated from the line.
It is often necessary in the administration of intravenous to a patient to know exactly how much fluid a particular patient has received over a given period of time. The amount and rate of fluid infused into the patient along with monitored changes in the patient""s condition can determine if additional infusions are indicated and how rapidly the fluids should be infused.
Devices which monitor the infusion of intravenous and irrigation solutions and provide a warning when such infusion has reached a predetermined extent are well known in the art. One group of devices makes use of a scale mechanism, such as a see-saw. When the amount of remaining fluid falls below some predetermined value, the see-saw tilts and actuates an electrical switch to trigger an alarm. Although the scale-based devices are simple, the springs used in the scales are quite sensitive to jolts or shocks that can occur, for example, if the patient accidentally strikes the device.
Another type of prior art device makes the use of a clip or clamp together with elements that complete an electrical signal circuit as the reservoir bag collapses on emptying. However, the clamp can effect the rate of flow of the IV fluid and the alerting signal is only activated when the reservoir is empty.
Many other devices utilize some form of spring extension which provides, in affect, a weighing of the slowly decreasing supply of fluid. In these devices a switch means is provided which actuates a warning signal when the weight of the fluid being administered has reached the desired level. These devices also experience sensitivity to jolts or shocks and can false alarm. Although these devices may initially provide accurate signaling capability, their inherent design principle of weight sensing by spring extension has failed to provide the requisite long-term accuracy. This failure is due to the ever-increasing fatigue of the spring caused by its repeated extension. Over a period of time this fatigue results in a change in the spring constant as the degree of fatigue increases.
Still other prior art devices use optical sensing equipment to sense the fluid level of the dripper and to monitor the fluid delivery system for occlusion or bubbles in the fluid. However, these devices have been found to be extremely complex and expensive. All known devices either monitor infusion rate or fluid empty condition.
Accordingly, there is a need for an infusion monitoring apparatus which can be used to monitor various infusion end-points, including monitoring predetermined infusion volumes and detecting almost empty infusion bags. Such an apparatus should also be able to detect very low or no flow conditions. Such an apparatus should not be sensitive to bumps or jolts, and should remain accurate over time. Such an apparatus should be easy to install and use by medical attendants. Moreover, such a device should be capable of being set to differing amounts of fluid infusion, and preferably calculate the rate of such infusion. The present invention fulfills these needs and provides other related advantages.
The present invention resides in an infusion monitoring apparatus which overcomes the shortcomings described above. The apparatus can be used as a monitor for any infusion where the bag is hanging, including gravity and infusion pump methods. The apparatus is particularly adapted for use in the gravity infusion environment.
The apparatus is comprised of a pole clamp extending from a housing and configured for removable attachment to a pole. An arm extends from the housing and has an end configured for holding an infusion fluid bag. Typically, the arm extends horizontally from the housing, generally opposite the pole clamp. An electronic weight sensing mechanism is disposed within the housing and associated with the arm. In a particularly preferred embodiment, the mechanism comprises a pair of magnets associated with the arm, and a Hall-effect sensor disposed within a gap between the magnets. Alternatively, the weight sensing mechanism comprises a load-cell associated with the arm. A control circuit, typically including a microprocessor, is electronically connected to the sensing mechanism for detecting a no-fluid-flow condition, a near empty bag condition, or a preselected amount of fluid loss condition. The apparatus is configured to always detect when a no-fluid-flow condition is present. The user may select to monitor and detect a pre-selected amount of fluid loss, such as 250 ml or 500 ml, otherwise, the apparatus monitors the infusion to detect and alarm when near-empty infusion condition occurs. Ideally, the infusion rate is monitored and displayed as well. The monitoring apparatus includes an alarm which is activated when the no-fluid-flow condition, the near empty bag condition, or the preselected amount of fluid loss condition has been detected. Preferably, the apparatus also includes a low battery alarm, for indicating battery replacement.
The process for monitoring gravity infusion into a patient generally comprises the steps of first hanging a fluid bag from the monitoring apparatus. The weight of the fluid bag is periodically measured, using the electronic weight sensing mechanism and the control circuit, to detect the no-fluid-flow condition, the near empty bag condition, or the preselected amount of fluid loss condition. An alarm is activated when any of these conditions are detected.
A near empty bag set point is set by hanging a weight from the monitor and apparatus and electronically saving the near empty bag set point weight. Typically, the near empty bag set point weight approximates an empty fluid infusion bag system, having a nominal amount of fluid therein. However, detection of the near empty condition is programmable to accommodate a range of infusion bags and setups as well as user preference. Users may wish to program the apparatus so that the near empty alarm is activated when the infusion bag has only 10-20 ml of remaining fluid, while others may wish to program the apparatus to alarm when there is an excess of 100 ml remaining in the infusion bag. Alternatively, a switch on the monitoring apparatus is depressed for selecting the monitoring of an amount of fluid to be infused totaling less than the fluid capacity of the fluid bag. For example, a 500 ml button can be depressed to select the monitoring of 500 ml of fluid to be infused.
Preferably, measuring includes the steps of taking multiple weight measurements over a short period of time and creating a reading, typically a linear-sloped reading, which is electronically saved. If the reading is within acceptable limits when compared to prior electronically saved readings, the reading is accepted. However, if it is determined that the reading is not within acceptable limits, additional weight measurements are taken over a short period of time to create a new reading if the immediately prior reading was without the acceptable limits.
The monitoring apparatus can be programmed such that an alarm is activated if no fluid loss is detected over a period of time. The monitoring apparatus can also be programmed to calculate and display the rate of fluid loss from the fluid bag.
In order to conserve power, the monitoring apparatus is maintained in a semi-inactive, battery conserving state and periodically self-activated to determine if a weight has been hung from the monitoring apparatus. Hanging a weight from the monitoring apparatus automatically activates the apparatus to its full operation.
The invention anticipates the use of a central station which monitors more than one monitoring apparatus. In such instance, a signal is transmitted from a monitoring apparatus to a remote electronic device to activate the alarm when the no-fluid-flow condition, the near empty bag condition, or the preselected amount of fluid loss condition has been detected.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.